Process for the separation of hydrocarbons



J. W. LATCHUM, JR

PRocEss FOR THE SEPARATION oF HYDRocARBoNs,

Filed Nov. 11, 1943 ac LvNollava d J. M w .n Y E E w m Tm. N N. H EW m O All V. T N NJ A v m. u Y B, mmwzmozoo t v m. .J H W V n n mm W I- o H l/O III Patented Dec. 11, 1945 V UNIT-ED STATES PATENT-orner PROCESS FOB SEPARATION OF I HYDROCARBONS John W. Latchum, Jr., Bartlesville', Okla., assignerv to Phillips Petroleum Company, a corporation of Delaware Application November 11, 1943, Serial No. 509,892

Claims.

This invention relates to the separation, puriiication, and recovery of hydrocarbons. More speciilcally, the invention relates to a process for thel erence fuelsfor use in determining the anti-knock ratings of the gasoline. The branched chain parflin 2,2,4-trimethylpentane is a standard of reference which has been given a value of 100 on the octane scale for determining the A. S. T. M. knock rating of motor fuels. 4In the rating of high octane aviation gasoline, tetraethyllead may be added to the 2,2,4-trimethylpentane. As a substitute for pure 2,2,4-trimethylpentane, speciiications `have been developed for a reference fuel which comprises a close boiling hydrocarbon fraction having a high concentration of 2,2,4-trimeth'ylpentane. The allowable content of unsaturated hydrocarbons is limited to 0.3 per cent maximum. An important object of this invention is to provide a process by which a closeboiling paramnic hydrocarbon fraction may be produced Cl. MiO- 676) to convert substantially all of the oleiin content to saturated hydrocarbons. hydrogenation, a loss in desirable product is sustained due to undesirable reactions which take place during the .hydrogenation The eiiiuen't of this hydrogenation step must be fractionated to remove undesirable hydrocarbons formed during the hydrogenation and having boiling points higher or lower than the maximum and minimum allowable in the finished reference fuel. The

present invention provides a process by which the unsaturated hydrocarbons may be removed without the disadvantageous results inherent in the hydrogenation procedureY The present invention involves anovel combination of fractionation andv treating withsulfurie acid by which a paraiinic fraction comprising substantially pure 2,2.4-trimethylpentane free from unsaturated hydrocarbons may be obtained. By the process of this invention the necessity for refractionation of the treated close boiling fraction, required in the hydrogenation procedure above mentioned; is obviated and little if any loss of desirable paraillns is sustained. A further which fraction contains little, if any, unsaturated hydrocarbons.

Present practice in the manufacture of reference fuel comprising chiefly 2,2,4-trimethy1pentane involves the following steps. The base stock is made by polymerization of isobutyleneto diisobutylene, and hydrogenating the diisobutylene to isooctane. Alternatively, isobutane may be reacted with isobutylene in an alkylation reaction to yield isooctane.. Both of 'the above reactions are now carried out in large scale operations to produce components for aviation gasoline. The

products of these reactions are rather complex .mixtures of hydrocarbons from which the ldesired aviation fuel blending stock is separated by a series of fractionation steps. After fractionation, the aviation gasoline blending stock' irom'a typical aviation gasoline contains roughly 25 Iper cent of 2,2,4-ti-imethylpentane.v Even after close i advantage of the present invention over the hy- 'drogenation procedure resides in the lower costs of construction and operation of equipment for obtaining the desired product. In accordance with the present invention,l the charge stock, which may be aviation gasoline blending stock containing- 2,2,4-trimethylpentane, is fractionated in 'iractionators suitable for the separation of a close boiling fraction from said stock. A stream of overhead product comprising 2,2,4-trimethylpentane in concentrated form is contacted with sulfuric acid of such concentration that substantially all of the'imsaturated hydrocarbons in the stream are absorbed. The reflux stream to the fractionator consists of the olefin-free eiliuent from the `sulfuric acid treatment. The reflux stream provided in this novel manner'aids in the separation of olefins having boiling points close to but higher than the boiling -point of 2,2,4-trimethylpentane It is, of course, old to refine petroleum by treatment with sulfuric acid, but' the primary object pf such treatment has'been to remove asphaltic compounds, sulfur compounds, and to lower the carbon residue, with the accompanying removal of unsaturates occurring as an objectionable side reaction. It is also oldl to remove the oleilns from hydrocarbon mixtures by absorbing the oleflns in sulfuric acid, but in this case the primary object has been to obtain the oleiins in a state suitable for further reactions, for example, hydrolysis to form alcohols or reaction with "aromatics to form alkyl derivatives. Likewise, the purification of a. paraiiin hydrocarbon by contacting it with concentrated sulfuric acid to remove small quantities of oleilns is a known procedure. The present invention involves a new-and unobvious use In carrying out the i line I to the fractionator it.

of sulfuric acid treatment of hydrocarbons for .removal of oleflns in combination with fractionation to obtain new and unexpected results.

Another object of this invention is to provide -an improved process for the separation of olens from parains.

Still another object o this invention is to provide a mproved process suitable for the manue of a close boiling hydrocarbon fraction comprising chiefly 2,2,4-trlmethylpentane sub- -stantially free from unsaturated hydrocarbons.

Other objects and advantages will be apparent from the following detailed description and the accompanying drawing in which like numerals designate` corresponding parts.

Figure 1 is a diagrammatic elevation of apparatus suitable for carrying out the present invention. y

Figure 2 is a diagrammatic elevationof a modification of apparatus for carrying out the present invention.

,With reference to' Figfl of the drawing, the I able means,l not shown in the drawing, for supplying heat to the column as is customary. Condensate from accumulator 8 is supplied to the column by line i@ in conventional manner. Uncondensed vapors and condensate may be re'- moved from the run tank or accumulator E through lines Il and l2, respectively. The fractionator d serves toremove from the feed stock as overhead the hydrocarbons lower boiling than the desired parain thereby determining the in'- itial boiling point of the final product.

Bottom product from fractionator d passes via The fractionator i6 may be of conventional design and provided with suitable means, not shown in the drawing. for supplying heat, as is customary. This frac- 'tionator serves to separate hydrocarbons having higher boiling points than the desired paraiiin from those boiling in the immediate vicinity of the boiling point of the desired parailin. The higher boiling hydrocarbons are removed from the base of the fractionating column by line il. The overhead vapors from the fractionator comprising the desired paraiiin in concentrated form,

together with other close boiling hydrocarbons not separable therefrom by conventional fractionation, pass via line l@ to the vessel i9. In the ves.- sel i9, thevapors are contacted with concentrated sulfuric acid. sulfuric acid of 65 to 98 per cent concentration is suitable. Generally, however, acid of 87 to 93 per cent is preferable. The vessel I 9 may be provided with bubble plates or packing to insure intimate contact between the acid and the'hydrocarbon vapor. The acid is circulated through line 2Q, withdrawing the acid from a point near the bottom of the vessel and introducing it at the top of the vessel for countercurrent contact with the hydrocarbon vapors. Fresh acid may be added and used acid removed, continuously or batchwise. The sulfuricv acid fre-1 moves the oleiins and any other unsaturated hy- A70 head vapors from fractionator i6 are passed to drocarbons present in the stream of hydrocarbon vapors,'by absorption, reaction, or both. Addition compounds formed by reaction with the sulfuric acid remain in the acid phase and tend to accumulate at the bottom of the vessel. The outlet line 2| is provided for removal of the acid and aseavao absorbed hydrocarbons, together with the reacation products formed, for disposal as waste or for further treatment as hereinafter discussed. The treated hydrocarbon vapors, free from unsaturated hydrocarbons,l .pass through line 23 from lwhich they may be passed through line 26 to the condenser 26 or through line 28 to the vessel 21 as controlled by the valves 28 and 29.

In many cases it is not necessary that the va- 10 pors leaving line 2d be' further treated. When it is essential that the nal product be completely free of sulfuric acid, the vapors are passed to the vessel 27 where they are contacted with a caustic solution in a manner analogous to that employed l5 `for acid treatment in vessel I9. From the vessel 27, the vapors may be passed through line 24 to the condenser or.through.line 30 to the vessel 3i as determined by the valves 32 and 33 vwhich control the flow to these lines. In the vessel @l the vapors are contacted with water to remove any caustic which may be carried inthe vapors after treatment in vessel 27. From the vessel 8l 'the vapors pass to condenser 25. Condensate col-7 lects in the run tank or accumulator 35 from 25 which product is withdrawn through line 35.

Condensate, consisting of paramns, free from unsaturated hydrocarbons, is passed through line 3l to the fractionator it as redux. n

Two important advantages of the present invention result from the use of olen-free hydrocarbons as reflux in the fractionator It. First, it improves the emciency of the fractionator by reducing the concentration of oleflns on the top trays of the fractionator to a value below that which would be present if the fractionating column were refluxed in conventional manner. This reduction in olefin concentration aids in the separation of olelns from paraflins-in the fractionator. This permits removal of a higher percentage, particularly of the higher boiling of the olens, in the bottoms from the fractionator. Second, the lower concentration of oleflns in the liquid at the top of the fractionator results in a lower concentration of olenns in the vapor passing overhead from the fractionator. This, in turn,

results in a savings in acid requirement in treat ing the fractionator overhead for' removal of olens. p The acid`treatment of the overhead of fracooctionator l@ removes unsaturated hydrocarbons without conversion of desired paramns .to undesirable hydrocarbons, i. e., hydrocarbons having boiling points higher or lower than the boiling range allowable in the product. Fractionation to meet A. S. T. M. distillation specifications maybe completed by the fractionators t and it' and the product removed through line 36 is, therefore, the completed product, .In contrast, hy- .drogenation of a hydrocarbon mixture, even though previously' fractionated to meet the distillation specification, produces by undesirable side reactions, -such as cracking, hydrocarbons which must be removedV by additional fractionation steps. The elimination oi the necessity for additional fractionation of the product is an important advantage of the present invention.

With reference to Fig. 2, the hydrocarbon feed stream is fractionated in fractionators 6 and I6 as described with reference to Fig.v 1. The overthe condenser d; the resulting condensate, co1- -lected in the accumulator or run tank M. Condensate from the run tank di iiows through line 52 and is admixed with sulfuric acid from line d3 in a centrifugal pump or other suitable mixf eenation efliuents.

. treated liquid, free from unsaturated hydrocar' bons, may be passed through the line 46 to the run tank or accumulator 41. Generally it is d esirable that the acid treatment be followed by a caustic wash to remove entrained acid. In this case the treated liquid from the vessel 45 is passed through the line 48, mixed with caustic solution from line 49 in the mixer 50', and introduced into the vessel I. In the vessel 5I the hydrocarbon stream separates from the caustic solution and may be passed tothe run tank 41 orto line 52 for, further treatment to remove caustic therefrom. If removal of caustic is desirable, the hydrocarbon stream is mixed with water from line 53 in the mixer 54 and passed to the water separator 55. After separation of the water from the hydrocarbons in vessel 55, the purified hydrocarbon stream is passed to the run tank 41. The product'is withdrawn through line 56 while a part of the olen-free hydrocarbon liquid from the run tank 41 is passed through line 51 to the fractionator I6 as reflux. The advantages of using a paraflinic hydrocarbon liquid reflux free from olens and other unsaturated hydrocarbons, have been previously cited in the discussion of Fig. 1. J'

This material was fractionated to give a feed stock boiling within the range of about 205 F. to about 215 F. `(The boiling point of pure 2,2,4-trimethylpentane is 210.3 F.) The feed stock was then hydrogenated using a nickel hydrogenation catalyst at '100 lbs. per sq. in. at a temperature within the range of about 400 to 600 F. to produce a product containing less than 0.3%

unsaturated hydrocarbons. The temperature atV the inlet to the catalyst was 400 to 500 F., at the outlet, 370 to 635 F. This product had to be refractionated 'to produce a product boiling within the range of about 205 to about 215 F. The overall loss bythis procedure amounted to 2.5 to 3.0% based on thefeed to the last mentioned dehydrogenation step. Thisloss maybe attributed to undesired reactions which take place simultaneously with lthe hydrogenation. principally the formation'olf butylenes which in turn are hydrogenated. n.,

The same starting material used in Example I was processed in accordance with the present invention.- The material was fractionated to meet boiling range specications by the l" A. S. T. M. distillation test and treated with The used acid from the acid treating step may be treated for regeneration of the acid, removal of the oleflns, or manufacture of by-products.

Such treatment forms no part of the present in,

Example I Aviation'gasoline blending stock is produced by polymerization` of isobutylene, hydrogenation of the polymer; and fractionation of .the hydro- The olefin content-sof this stock ranges from 0.4% to 1.0% depending upon the operation of the hydrogenation unit and the I length of time the catalystis on stream. With pressure of 2.5 lbs. per sq. in. at 100' F. 'Ihe sulfuric acid for removal of unsaturated hydrocarbons. The acid treatment was carried out at substantially atmospheric pressure. The overall loss by this method amounted to about 1.5% of the hydrocarbon stream passed to the sulfuric acid treatment. yThe product does not require further fractionation.

Another important advantage of the present close boiling oleflns, contacting said stream with sulfuric acid of suillcient concentration to remove substantially ali olensfrom said stream,

ywithdrawing a part of the resulting treated hydrocarbon stream as product, and passing' a part vof said-treated stream of hydrocarbons in liquid phase to the kfractional distillation as reflux therefor.

2. The process of c'laim 1 in which the concentration of sulfuric acid is within the range of 3. The process of claim 1 in which the concentration of sulfuric acid is within the range of A. S. 'I'. M. distillation is as follows:

o F. Initial boiling point-; 172 5 per cent evaporated-.. -4. 186 10 per cent evaporated i 190 20 percent evaporated f- 196 30 per cent evaporated -200 40 per cent evaporated 204 50 per cent evaporated 210 60 per cent evaporated 216 '70 per cent evaporated 228 per cent evaporatedg.; -r-f 250 per cent evaporated.; 320. per cent evaporated 336 End point ing not more than about 0.3 per cent of unsatu rated hydrocarbons, which comprises fractionally distilling a normally'liquld aliphatic hydrocarbon mixture resulting from polymerization of butylenes and hydrogenation of the resultingl 354 75 polymer to produce a stock having an olefin 1 wherein said over-.

substantially all olens from said liquidunder conditions such that the liquid hydrocarbon efuent from said contacting contains not more than 0.3".per cent ci' unsaturated hydrocarbons, withdrawing a part of the resulting treated pai'- atlinic hydrocarbon liquid as a product, and passing a further portion of said treated paraflinic' hydrocarbon liquid in liquid phase to said iractional distillation as reuxftherefor.

JOHN W. LATCHUM, JR. 

